1. Field
Embodiments of the present invention relate generally to rolling mills in which successive billet lengths of a hot rolled product are formed into rings by a laying head, and are concerned more particularly with a method of operating a conveyor employed to transport the rings from the laying head to a remote reforming station where the rings are gathered into coils.
2. Description of Related Art
In a conventional rolling mill, as depicted schematically in FIG. 1, a preheated billet is hot rolled into a rod in a succession of roll stands, the last of which is depicted at 8. The hot rolled product is formed into rings “R” by a laying head 10, and the rings are deposited on a conveyor 12 for transport in an overlapping pattern to a remote reforming station 14 where the rings are gathered into coils. A typical modern day rolling mill can produce rod at a rate per strand of up to 160 tons/hour, with the rod being gathered at the reforming station into coils weighing 1.8 tons or more.
The time gap between billets is typically about 5 seconds, and the time to roll a coil of 1.8 tons at 160 tons/hr is approximately:
      160    ⁢          /        ⁢    1.8    =            88.9      ⁢                          ⁢      and      ⁢                          ⁢              3600        88              =          40.5      ⁢                          ⁢              sec        .            
Normally, it takes about 15 seconds to clear a completed coil from the reforming station, during which time some of the rings of the next billet length must be temporarily accumulated above the reforming chamber. Thus, taking into account the 5 second gap between billets, approximately 25% (15-5/40.5) of the coil must be suspended and then dropped into the reforming chamber at the beginning of the next coil forming cycle.
Experience has shown that dropping this amount of product into the reforming chamber at the beginning of each coil forming cycle can distort the coil base, resulting in an unstable coil. Moreover, maintaining a 5 second gap between billets can result in a loss of up to 10% of mill utilization time.